Testing strategies for water treeing

The harmonisation of tests for the European market has been an incentive to produce a test procedure suitable for use by suppliers and users of polymeric insulated cable. In the case of wet designs of polymeric insulated cables the test methods being considered have become more ambitious than establishing a quality of the product but have become centred on the deterioration in service caused by water tree deterioration. This emphasis on service deterioration arises from some incidences of failures in service. More than 20 test proposals are being considered by CENELEC for a European test. This paper briefly mentions the range of proposed tests. Basically the tests consist of exposing the cable to water and electrical field for a sufficient time to grow water trees which are large enough to influence the breakdown strength of the cable. The breakdown strength can be assessed at periods during the ageing. An alternative strategy is that the cable survives the ageing period